Bidirectional adjustable magneto-rheological inerter damper

Abstract

The invention relates to the field of electromagnetic vibration damping devices for changing fluid viscosity and adjusting damping properties, in particular to a bidirectional adjustable magneto-rheological inerter damper. The bidirectional adjustable magneto-rheological inerter damper comprises a first terminal (11), a second terminal (12), a first end plate (21) and a second end plate (22), and is characterized by further comprising a screw (3), screw balls (41), channel balls (42), an input ring (51), an output ring (52), a continuously variable transmission (6) and a controllable damping system (7), and the continuously variable transmission (6) comprises a stator (61), an idle wheel (62), a shell (65), traction fluid (66) and the like. And the controllable damping system (7) comprises a fixed pipe (71), a fixed pipe rotor (72), a rotor bearing (73), a flywheel (76), an electromagnetic coil group (77), a controller (78) and a direct-current power supply (79). Space is saved, and the vibration control performance is good.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic vibration reduction devices for adjusting damping properties by changing fluid viscosity, in particular to a bidirectionally adjustable magnetorheological inertial capacity damper. Background Art

[0002] In the field of vibration control research, how to suppress the vibrations generated by building structures, mechanical vehicles, equipment, etc. when they are impacted by fluctuations of different frequencies is a severe challenge. In this regard, passive control devices are often used as a means of vibration control in buildings and machinery.

[0003] However, the main disadvantage of passive control devices is the limited operating frequency range, while the actual external excitation may have different frequencies in each time period. For traditional passive devices based on mass and inertia vessels, when subjected to external excitation, their natural frequency is close to the natural frequency of the main structure, vehicle or machine, and can only cover a narrow frequency band. In addition, passive devices may produce detuning effects when subjected to excitations with time-varying frequencies, resulting in a decrease in the vibration reduction performance of the device.

[0004] In summary, in order to protect the safety of building structures, machinery, etc. under vibration, broaden the effective frequency band of vibration control devices, and make the devices suitable for civil engineering buildings, as well as for mechanical equipment and other fields, it is necessary to propose an adaptive bidirectional parameter-adjustable damper using smart materials. Summary of the invention

[0005] In order to overcome the defects of the prior art and provide a vibration reduction device which saves space and has good vibration controllability, the present invention discloses a bidirectionally adjustable magnetorheological inertia damper.

[0006] The present invention achieves the purpose of the invention through the following technical solutions: A bidirectional adjustable magnetorheological inertial damper comprises a first terminal, a second terminal, a first end plate and a second end plate, wherein the first terminal is fixed to a sensing system to be controlled via the first end plate, and the second end plate is connected to a controlled system (such as a building structure or a mechanical / vehicle device) via the second terminal, and the first end plate and the second end plate are parallel to each other, and the device is characterized in that it also comprises a screw, a screw ball, a groove ball, an input ring, an output ring, a stepless transmission and a controllable damping system. The first end plate is fixed to one end of the screw rod, the screw rod is arranged horizontally, the first end plate and the screw rod are perpendicular to each other, the nut is screwed on the thread of the screw rod, one end of the nut is facing the first end plate, a screw ball is arranged in the groove of the thread meshing with the nut, the screw ball fills the thread meshing with the nut one by one along the groove of the thread, the other end of the nut on the screw rod is arranged with an input ring, a stepless transmission and an output ring in sequence, and the central axes of the screw rod, the input ring and the output ring coincide with each other; The continuously variable transmission includes a stator, an idler, an idler bearing, an idler rotor, a housing and a traction fluid. The stator is a hollow cylindrical shell, and the stator is sleeved on the screw; The idler wheel is a hollow cylindrical shell, and the idler wheel is rotatably sleeved on the stator; The inner ring hoop of the idler wheel bearing is arranged on the idler wheel, and bearing balls are arranged between the inner ring and the outer ring of the idler wheel bearing; The idler rotor hoop is arranged on the outer ring of the idler bearing; The outer shell is a hollow cylindrical shell, and the inner wall of the outer shell is provided with at least three grooves which are parallel to the outer shell generatrix or form an acute angle and are parallel to each other, and the grooves are evenly distributed around the central axis of the outer shell. The outer shell is sleeved on the screw, and the two ends of the stator are respectively fixed to one end face of the outer shell; The diameter of the groove ball and the aperture of the groove match each other, a through hole is provided on one diameter of the groove ball, there are at least three ball shafts, each ball shaft is inserted into a through hole of the groove ball and the groove ball rotates around the ball shaft, both ends of each ball shaft are fixed on an end face of the shell, and the groove ball is embedded between the idler rotor and the shell; The central axes of the screw, stator, idler, idler bearing, idler rotor and housing coincide with each other; The groove balls are located at two sides of the ball shaft and are respectively connected to a fixed input ring and an output ring. A traction fluid is poured between the input ring and the groove balls. The traction fluid is silicone oil. The controllable damping system includes a fixed tube, a fixed tube rotor, a rotor bearing, a magnetorheological fluid, a sealing material, a flywheel, an electromagnetic coil group, a controller and a DC power supply. One end of the fixed tube is sleeved on the screw and connected to the fixed shell, the other end of the fixed tube is connected to the fixed second end plate, the fixed tube rotor is sleeved outside the fixed tube through two rotor bearings, the gap between the fixed tube rotor and the fixed tube is filled with magnetorheological fluid and the gap is sealed with sealing material to prevent leakage of the magnetorheological fluid, the magnetorheological fluid is Magnetorheological Fluid, referred to as MR fluid, which is a suspension composed of soft magnetic particles, carrier fluid and additives, the flywheel is sleeved outside the output ring, the stepless transmission and the input ring, and the flywheel and the output ring are connected and fixed, at least four electromagnetic coil groups are wound outside the fixed tube to generate a controllable magnetic field, and the controller is respectively connected to the shell, the electromagnetic coil group and the DC power supply through wires to transmit a small current of no more than 5A provided by the DC power supply to the electromagnetic coil group.

[0007] The bidirectionally adjustable magnetorheological inertia damper is characterized by: The inner wall of the housing is provided with six grooves which are parallel to the housing generatrix or form an acute angle with the generatrix and are parallel to each other; The DC power supply should be a battery or an uninterruptible power supply.

[0008] The bidirectionally adjustable magnetorheological inertia damper is characterized by: The groove balls and the housing rotate in the same direction, while the groove balls and the idler rotor rotate in opposite directions.

[0009] In the present invention, the screw, nut and screw ball form a screw ball system, and the screw ball in the thread is rotated to convert the translation of the screw into the rotation of the nut. This reaction motion is in two opposite directions, forward and backward, and is accompanied by slight friction. The stator, idler, idler bearing, idler rotor, housing and traction fluid constitute a continuously variable transmission. Through the variable mass amplification effect of inertia achieved by the smooth energy transmission of the continuously variable transmission, the speed of the continuously variable transmission is variable and controllable without stopping. A fixed tube, a fixed tube rotor, a rotor bearing, a magnetorheological fluid, a sealing material, a flywheel, an electromagnetic coil group, a controller and a DC power supply constitute a controllable damping system. The DC power supply inputs a small current to the electromagnetic coil group to generate a controllable magnetic field. When the magnetorheological fluid passes through the magnetic field, the viscosity and damping of the magnetorheological fluid will change. In order to improve the performance, the arrangement, number and radius of the coils can be changed.

[0010] The rotation of the flywheel is controlled by the continuously variable transmission through the rotation of the output ring to provide controllable inertia and related inertia force. The rotation resistance of the fixed tube rotor is controlled by the controllable damping system (7) to obtain controllable damping and damping force.

[0011] The present invention has the following beneficial effects: 1. The inertia damper of the present invention can simultaneously control the bidirectional vibration of buildings, machinery, etc. in a plane, and has the advantages of saving building space, saving the amount of dampers, reducing the concentrated load on the floor and saving costs.

[0012] 2. The inertia capacity damper of the present invention can be connected to the ball screw system through a continuously variable transmission, and the transmission ratio of the continuously variable transmission can be adjusted in real time according to the electrical signal input by the controller, thereby adjusting the inertia capacity. Therefore, it has better two-way vibration control performance than the traditional inertia capacity damper.

[0013] 3. The inertia damper of the present invention can adjust the magnetic field strength of the magnetorheological fluid material in real time according to the electrical signal input by the controller, and then adjust the damping of the damper in real time, so it has better bidirectional vibration control performance than traditional dampers.

[0014] 4. In addition to its strong energy dissipation capability, the inertial capacitance damper of the present invention can also adjust its frequency to an optimal value, thereby effectively reducing the vibration to which the device is subjected in construction or mechanical applications.

[0015] 5. The inertia capacity damper of the present invention can achieve good vibration reduction effect in a wider external excitation frequency band, broaden the application range of the inertia capacity damper, and improve its vibration reduction performance and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a front view of the present invention, Figure 2 yes Figure 1 AA section view, Figure 3 is an assembly diagram of the continuously variable transmission of the present invention, Figure 4 is the operating principle diagram of the continuously variable transmission in the present invention, Figure 5 is the operating principle diagram of the controllable damping system in the present invention, Figure 6 is an axonometric diagram of the controllable damping system of the present invention, Figure 7 It is a schematic diagram of the assembly of the controllable damping system in the present invention.

[0017] The component names corresponding to the reference numerals are as follows: 11: First terminal, 12: Second terminal, 21: First end plate, 22: Second end plate, 3: Screw, 31: thread, 32: Nut, 41: Screw ball, 42: groove ball, 421: ball bearing, 51: Input ring, 52: Output ring, 6: Stepless transmission, 61: stator, 62: Idler pulley, 63: Idler bearing, 64: Idler rotor, 65: Shell, 651: slot, 66: Traction fluid, 7: Controllable damping system, 71: Fixed pipe, 72: Fixed tube rotor, 73: rotor bearing, 74: Magnetorheological fluid, 75: Sealing material, 76: Flywheel, 77: Solenoid coil assembly, 78: Controller, 79: DC power supply. DETAILED DESCRIPTION

[0018] The present invention is further described below by means of specific examples.

[0019] Example 1 A bidirectional adjustable magnetorheological inertia damper comprises a first terminal 11, a second terminal 12, a first end plate 21, a second end plate 22, a screw 3, a screw ball 41, a groove ball 42, an input ring 51, an output ring 52, a stepless transmission 6 and a controllable damping system 7, such as Figure 1 to Figure 7 As shown, the specific structure is: The first terminal 11 is fixed to the induction system to be controlled through the first end plate 21, and the second end plate 22 is connected to the controlled system (such as a building structure or a mechanical / vehicle equipment) through the second terminal 12, and the first end plate 21 and the second end plate 22 are parallel to each other; The first end plate 21 is fixed to one end of the screw rod 3, the screw rod 3 is arranged horizontally, the first end plate 21 and the screw rod 3 are perpendicular to each other, the nut 32 is screwed on the thread 31 of the screw rod 3, one end of the nut 32 is facing the first end plate 21, and a screw ball 41 is arranged in the groove of the thread 31 meshing with the nut 32, and the screw ball 41 fills the thread 31 meshing with the nut 32 one by one along the groove of the thread 31, and the other end of the nut 4 on the screw rod 3 is provided with an input ring 51, a stepless transmission 6 and an output ring 52 in sequence, and the central axes of the screw rod 3, the input ring 51 and the output ring 52 coincide with each other; The continuously variable transmission 6 includes a stator 61, an idler wheel 62, an idler wheel bearing 63, an idler wheel rotor 64, a housing 65 and a traction fluid 66. The stator 61 is a hollow cylindrical shell, and the stator 61 is sleeved on the screw 3; The idler wheel 62 is a hollow cylindrical shell, and the idler wheel 62 is rotatably sleeved on the stator 61; The inner ring hoop of the idler wheel bearing 63 is arranged on the idler wheel 62, and bearing balls are arranged between the inner ring and the outer ring of the idler wheel bearing 63; The idler rotor 64 is hooped on the outer ring of the idler bearing 63; The housing 65 is a hollow cylindrical shell, and the inner wall of the housing 65 is provided with at least three grooves 651 which are parallel to the generatrix of the housing 65 or form an acute angle and are parallel to each other. The grooves 651 are evenly distributed around the central axis of the housing 65. The housing 65 is sleeved on the screw 3, and the two ends of the stator 61 are respectively fixed to one end surface of the housing 65. The diameter of the groove ball 42 matches the aperture of the groove 651. A through hole is provided on one diameter of the groove ball 42. There are at least three ball shafts 421. In this embodiment, six ball shafts 421 are provided. Each ball shaft 421 is inserted into a through hole of the groove ball 42 and the groove ball 42 rotates around the ball shaft 421. Both ends of each ball shaft 421 are fixed on an end surface of the housing 65, and the groove ball 42 is embedded between the idler rotor 64 and the housing 65. The central axes of the screw 3, the stator 61, the idler 62, the idler bearing 63, the idler rotor 64 and the housing 65 coincide with each other; The two sides of the groove ball 42 at both ends of the ball shaft 421 are respectively connected to the fixed input ring 51 and the output ring 52, and the traction fluid 66 is poured between the input ring 51 and the groove ball 42, and the traction fluid is selected from silicone oil; The controllable damping system 7 includes a fixed tube 71, a fixed tube rotor 72, a rotor bearing 73, a magnetorheological fluid 74, a sealing material 75, a flywheel 76, an electromagnetic coil assembly 77, a controller 78 and a DC power supply 79. One end of the fixed tube 71 is sleeved on the screw 3 and connected to the fixed housing 65, and the other end of the fixed tube 71 is connected to the fixed second end plate 22. The fixed tube rotor 72 is sleeved on the outside of the fixed tube 71 through two rotor bearings 73. The gap between the fixed tube rotor 72 and the fixed tube 71 is filled with magnetorheological fluid 74 and the gap is sealed with a sealing material 75 to prevent leakage of the magnetorheological fluid 74. The magnetorheological fluid 74 is Magnetorheological Fluid, referred to as MR fluid, and is a suspension composed of soft magnetic particles, carrier fluid and additives. The flywheel 76 is sleeved on the outside of the output ring 52, the stepless transmission 6 and the input ring 51, and the flywheel 76 and the output ring 52 are connected and fixed. At least four electromagnetic coil groups 77 are wound around the outside of the fixed tube 71 to generate a controllable magnetic field. The controller 78 is respectively connected to the housing 65, the electromagnetic coil group 77 and the DC power supply 79 through wires to transmit a small current of no more than 5A provided by the DC power supply 79 to the electromagnetic coil group 77. The DC power supply 79 is a battery or an uninterruptible power supply.

[0020] In this embodiment, the groove balls 42 and the housing 65 rotate in the same direction, and the groove balls 42 and the idler rotor 64 rotate in opposite directions.

[0021] In this embodiment: the screw 3, the nut 32, and the screw ball 41 form a screw ball system. By rotating the screw ball 41 in the thread 31, the translation of the screw 3 is converted into the rotation of the nut 32. This reaction motion is in two opposite directions, forward and backward, and is accompanied by slight friction. In other words, the interaction between the screw ball 41 and the thread 31 causes the forward and backward translation of the screw 3 to be converted into the reciprocating rotation of the nut 32. There is a rigid connection between the nut 32 and the input ring 51 of the continuously variable transmission 6, so that the rotation amount and rotation direction of the nut 32 and the input ring 51 are exactly the same.

[0022] The stator 61, the idler wheel 62, the idler wheel bearing 63, the idler wheel rotor 64, the housing 65 and the traction fluid 66 constitute a continuously variable transmission 6. Through the variable mass amplification effect of inertia achieved by the smooth energy transmission of the continuously variable transmission 6, the speed of the continuously variable transmission 6 is variable and controllable without stopping.

[0023] The fixed tube 71, the fixed tube rotor 72, the rotor bearing 73, the magnetorheological fluid 74, the sealing material 75, the flywheel 76, the electromagnetic coil group 77, the controller 78 and the DC power supply 79 constitute a controllable damping system 7. The DC power supply 79 inputs a small current to the electromagnetic coil group 77 to generate a controllable magnetic field. When the magnetorheological fluid 74 passes through the magnetic field, the viscosity and damping of the magnetorheological fluid 74 will change. In order to improve the performance, the arrangement, number and radius of the coils can be changed.

[0024] The rotation of the flywheel 76 is controlled by the CVT 6 through the rotation of the output ring 52 to provide controllable inertia and related inertial force, and the rotational resistance of the fixed tube rotor 72 is controlled by the controllable damping system 7 to obtain controllable damping and damping force.

[0025] The continuously variable transmission 6 transmits power in the following manner: the input ring 51 connected to the groove balls 42 receives the rotational motion input from the nut 32, which is then transmitted to the groove balls 42. Subsequently, the output ring 52, which is also in contact with the groove balls 42, is subjected to the rotational force of the groove balls 42 and transmits the tuned required rotational power to the fixed tube rotor 72 and the flywheel 76.

[0026] The operating principle of the continuously variable transmission 6 is as follows Figure 4 As shown: due to the rotation of the input ring 51, the groove balls 42 can rotate around their respective ball shafts 421. In addition, through the power supply of an external low-voltage motor, the idler wheel 62 and the idler rotor 64 can move linearly relative to the stator 61, so that the ball shaft 421 can be tilted relative to the central axis of the housing 65. The process of changing the inclination angle of the ball shaft 421 through the linear movement of the idler wheel 62 and the idler rotor 64 is called the continuously variable transmission ratio φ adjustment, which is specifically characterized by the speed ratio between the output ring 52 and the input ring 51.

[0027] The result of the CVT 6 ratio adjustment is to change the angular velocity and torque transmission, thereby determining Figure 4 The input radius rin and the output radius rout in the CVT 6. The transmission of energy and rotation is carried out in three transmission ratio modes of the CVT 6, namely neutral when φ=1, low speed when φ<1 and overspeed when φ>1. The output speed in the three transmission ratio modes should be equal to, lower than and higher than the input speed, respectively. The transmission ratio range of the CVT 6 can reach 0.45 to 2.2. Within this range, the efficiency of the equipment can be improved by designing the CVT 6, such as modifying the number and diameter of the groove balls 42. In addition to being able to transmit energy accurately, continuously and uninterruptedly, the CVT 6 can also withstand and transmit large external torques.

[0028] like Figure 5 As shown in FIG. 1 , a layer of magnetorheological fluid 74 is injected into the small gap between the fixed tube rotor 72 and the fixed tube 71. The electromagnetic coil assembly 77 is installed around the fixed tube 71 to generate a controllable magnetic field, such as Figure 5 As shown in B. By supplying current to the electromagnetic coil group 77, a magnetic field is formed around the fixed tube 71, and the magnetic field strength can be adjusted by adjusting the input current. By activating a variable magnetic field perpendicular to the rotation direction of the magnetorheological fluid 74, the viscosity and damping coefficient of the magnetorheological fluid 74 can be adjusted. The mechanism of the magnetorheological system in the controllable damping system 7 is based on the shear-type resistance flow of the magnetorheological fluid 74 in the magnetic field generated by the electromagnetic coil group 77. Finally, a translational variable damping force in the opposite direction of the external force is generated by the shear-type magnetorheological system of the controllable damping system 7.

[0029] like Figure 6 As shown in the figure: by respectively utilizing the "variable mass amplification effect of inertia achieved through the smooth energy transmission of the continuously variable transmission" and the "variable damping effect achieved through the shear-type flow of the magnetorheological fluid in the magnetic field generated by the electromagnetic coil", a new independent variability of inertia and damping can be achieved at the same time. The characteristic of this embodiment is that a continuously variable transmission 6 is used as the first regulator to produce a controllable and non-stop continuously variable speed control system with variable speed, and a magnetorheological fluid 74 with an electromagnetic coil group 77 is added as the second regulator to produce variable damping. In addition, a controller 78 is also used to adjust the optimal value of inertia and damping according to the input signal. The controller 78 transmits a small current provided by a DC power supply 79 to the continuously variable transmission 6 and the electromagnetic coil group 77 through a wire. Therefore, the transmission ratio and the value of the magnetic field strength of the continuously variable transmission 6 will change according to the received current, and finally provide variable inertia and damping.

[0030] The assembly diagram of this embodiment is as follows Figure 7 shown.

Claims

1. A bidirectionally adjustable magnetorheological inertial damper, comprising a first terminal (11), a second terminal (12), a first end plate (21) and a second end plate (22), wherein the first terminal (11) is fixed to an induction system to be controlled via the first end plate (21), the second end plate (22) is connected to the controlled system via the second terminal (12), the first end plate (21) and the second end plate (22) are parallel to each other, and wherein: It also includes a screw (3), a screw ball (41), a groove ball (42), an input ring (51), an output ring (52), a stepless speed changer (6) and a controllable damping system (7). The first end plate (21) is fixed to one end of the screw rod (3), the screw rod (3) is arranged horizontally, the first end plate (21) and the screw rod (3) are perpendicular to each other, the nut (32) is screwed on the thread (31) of the screw rod (3), one end of the nut (32) is directly opposite to the first end plate (21), a screw ball (41) is arranged in the groove of the thread (31) meshing with the nut (32), the screw ball (41) fills the thread (31) meshing with the nut (32) one by one along the groove of the thread (31), the other end of the nut (4) on the screw rod (3) is provided with an input ring (51), a stepless transmission (6) and an output ring (52) in sequence, and the central axes of the screw rod (3), the input ring (51) and the output ring (52) coincide with each other; The continuously variable transmission (6) comprises a stator (61), an idler wheel (62), an idler wheel bearing (63), an idler wheel rotor (64), a housing (65) and a traction fluid (66). The stator (61) is a hollow cylindrical shell, and the stator (61) is sleeved on the screw (3); The idler wheel (62) is a hollow cylindrical shell, and the idler wheel (62) is rotatably sleeved on the stator (61); The inner ring hoop of the idler wheel bearing (63) is arranged on the idler wheel (62), and bearing balls are arranged between the inner ring and the outer ring of the idler wheel bearing (63); The idler rotor (64) is hooped on the outer ring of the idler bearing (63); The outer shell (65) is a hollow cylindrical shell. The inner side wall of the outer shell (65) is provided with at least three grooves (651) which are parallel to the generatrix of the outer shell (65) or form an acute angle with each other. The grooves (651) are evenly distributed around the central axis of the outer shell (65). The outer shell (65) is sleeved on the screw (3). The two ends of the stator (61) are respectively fixed to one end surface of the outer shell (65). The diameter of the groove ball (42) and the aperture of the groove (651) match each other, a through hole is provided on one diameter of the groove ball (42), there are at least three ball shafts (421), each ball shaft (421) is respectively inserted into a through hole of the groove ball (42) and enables the groove ball (42) to rotate around the ball shaft (421), both ends of each ball shaft (421) are respectively fixed on an end surface of the housing (65), and the groove ball (42) is embedded between the idler rotor (64) and the housing (65); The central axes of the screw (3), the stator (61), the idler wheel (62), the idler wheel bearing (63), the idler wheel rotor (64) and the housing (65) coincide with each other; The two side surfaces of the groove balls (42) at both ends of the ball shaft (421) are respectively connected to a fixed input ring (51) and an output ring (52), and a traction fluid (66) is injected between the input ring (51) and the groove balls (42); The controllable damping system (7) comprises a fixed tube (71), a fixed tube rotor (72), a rotor bearing (73), a magnetorheological fluid (74), a sealing material (75), a flywheel (76), an electromagnetic coil assembly (77), a controller (78) and a DC power supply (79). One end of the fixed tube (71) is sleeved on the screw rod (3) and connected to the fixed housing (65), and the other end of the fixed tube (71) is connected to the fixed second end plate (22). The fixed tube rotor (72) is sleeved outside the fixed tube (71) through two rotor bearings (73). A magnetorheological fluid (74) is injected into the gap between the fixed tube rotor (72) and the fixed tube (71), and the gap is sealed with a sealing material (75). The flywheel (76) is sleeved outside the output ring (52), the stepless transmission (6) and the input ring (51), and the flywheel (76) and the output ring (52) are connected and fixed. At least four electromagnetic coil groups (77) are wound outside the fixed tube (71), and the controller (78) is respectively connected to the housing (65), the electromagnetic coil group (77) and the DC power supply (79) through wires to transmit a small current provided by the DC power supply (79) to the electromagnetic coil group (77).

2. The bidirectionally adjustable magnetorheological inertia damper according to claim 1 is characterized in that: The inner side wall of the housing (65) is provided with six grooves (651) which are parallel to the generatrix of the housing (65) or form an acute angle with the generatrix of the housing (65) and are parallel to each other; The DC power source (79) is selected from a storage battery or an uninterruptible power supply.

3. The bidirectionally adjustable magnetorheological inertia damper according to claim 2 is characterized in that: The groove ball (42) and the housing (65) rotate in the same direction, while the groove ball (42) and the idler rotor (64) rotate in opposite directions.

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